Hidróxidos duplos lamelares intercalados com o ânion glifosato: preparação, caracterização e estudo de liberação controlada de glifosato em solução aquosa

Abstract

In this work were prepared by coprecipitation and characterized by powder XRD and FTIR compounds of the hydrotalcite type, known as Layered Double Hydroxides (LDH), intercalated with the glyphosate anion (GLYP), and the conditions of preparation and the stoichiometric ratio Mg:Al:GLYP were studied. The best condition observed was under reflux for 30 hours and stoichiometric ratio 2: 1: 1 for Mg+2, Al+3 and GLYP, as indicated by the characteristic bands of LDH intercalated with glyphosate and no other bands present, which could be assigned to other intercalated ions or to free glyphosate. Under those preparation conditions the LDH interlamellar spacing was 0.62 nm, compatible with the intercalation of glyphosate. The controlled release of glyphosate was studied using ion exchange reactions of Layered Double Hydroxides containing glyphosate with an aqueous medium containing carbonate, chloride or nitrate anions. In those cases the glyphosate was quantified spectrophotometrically by Ruhemann's purple method (max = 570 nm), and the initial releasing rates of 0.65 mg/ml/h (carbonate), 0.14 mg/ml/h (nitrate) and 0.08 mg/ml/h (chloride) were measured. Regarding the XRD patterns of the ion-exchanged products, it was observed that the structure of HDL was maintained, but with the reduction of the interlayer spacing in all cases, having a sufficient size for the anion of the involved ion exchange, but not enough for the presence of GLYP, demonstrating so that the exchange was successful.